#include <iostream.h>
# include <fstream.h>

void main()
{long a[2000001];
  long n,i,j,nr;

fstream f("ciur.in",ios::in);
fstream g("ciur.out",ios::out);
f>>n;
f.close();

for (i=2; i<=n; i++) a[i]=1;

for (i=2; i<=n/2; i++)
if (a[i]==1)
 for (j=i+i; j<=n; j+=i)
   a[j]=0;

for (nr=0,i=2; i<=n; i++)
if (a[i]==1) nr++;
g<<nr;

g.close();

}